Such an under-sea optical cable has a central optical module and strength armoring surrounding the optical module. The optical module is formed by a bundle of optical fibers disposed freely inside a metal protective tube covered with an insulating sheath referred to as the "cable inner sheath." The protective tube is made of stainless steel, in particular. The inner sheath is made of polyethylene. The armoring wires are preferably disposed in at least two layers around the optical module. They give the cable suitable mechanical resistance to traction, and optionally they form a pressure-resisting vault. They are commonly covered with a conductive strip, generally made of copper, wound or welded lengthwise, which strip is used for electrically powering equipment such as repeater-regenerators interposed on the optical link defined by the set of interconnected cables. A protective outer sheath covers each cable.
For the purposes of connecting together two such cables, the component parts of the cables are separated from one another along the end portions to be connected together. In this way, the protective tubes for protecting the bundles of fibers and the inner sheaths are cut at different lengths from the ends so as to leave the bundles of fibers projecting from the protective tubes. The bundles of fibers are also left projecting to a greater or lesser extent relative to the ends of the inner sheaths. The armoring wires are not cut, or they are cut only over a short length, but they are unstranded over a length that is sufficient for the optical modules to be connected together. The conductive strips are cut over the length of the unstranded armoring wires. The outer sheaths are also cut, leaving the conductive strips to project slightly therefrom.
In most of the splice devices currently made, the two bundles of fibers of the two cables are spliced together by using a monofiber splicing technique. That technique entails leaving each fiber of each bundle to project over a considerable length, and storing the surplus lengths of the two bundles of fibers in the splice device, which is thus rendered relatively complex and bulky.
Compared with the preceding technique, the multifiber welding technique now in use advantageously enables the two bundles of fibers to be spliced together in a single operation. This technique further requires only a short surplus length to be left on each bundle of fibers. The multifiber welding technique also enables a single auxiliary tube to be used for protecting the multifiber weld, the auxiliary tube extending between the protective tubes for protecting the bundles of fibers, and being secured to said protective tubes.
Document U.S. Pat. No. 5,076,657 describes a method and a structure for interconnecting optical fibers in metal protective tubes, using such an auxiliary tube welded to the ends of the metal protective tubes, so as to protect the fiber weld. That document also discloses that the auxiliary tube is put under elongation so that it extends from one protective tube to the other, and is then welded to said protective tubes, so as to prevent the protected fiber weld from being subjected to any subsequent traction forces that may degrade the optical transmission characteristics.
Putting the auxiliary tube under elongation is a lengthy operation and is difficult to monitor. It may further create weak points along the auxiliary tube or at the welds between the ends thereof and the ends of the protective tubes.
Document GB-A- 2 030 723 describes a splice between two optical cables whose optical fibers are disposed in protective tubes, with the protective tube in each cable being surrounded by one or more layers of armoring wires. In that document, the ends of the optical fibers of the two cables are welded together and are covered by a ferrule formed by two half-shells locked facing each other, the ferrule having threaded ends. The ends of the armoring wires are tensioned and clamped between conical parts received in the ends of the ferrule, and are locked thus by two end nuts screwed on the threaded ends of the ferrule.